All about descriptions
Descriptions are a must. You need them for any type of writing beyond the barest drabbles. Involve the reader in the piece. And that means pulling descriptive prose out of your head. You must commit it to paper or pixels.
Scene setting is covered elsewhere in this blog. However, that’s closely related to your descriptive abilities. Consider what is important.
Describe human beings as soon as you can. Unless the character’s appearance is some sort of spoiler, you should get their basics down quickly. Otherwise, your readers will picture one thing and, when they are told something different about the character, it will feel jarring to them. If I think your Mary character is Asian, and then you later (finally!) tell me she’s a blonde, that has the potential to take me right out of the story.
I’ll blog about describing people of color elsewhere. For now, just concentrate on basic descriptors. Those are, generally: gender, age range, height, body size and shape, hair color (or baldness), facial hair if appropriate, and eye color. Furthermore, add any unique identifiers. These are a disability or tattoos or the like.
Think about what is normally considered in a standard police lineup. For example, police officers can’t conduct an overly suggestive American police lineup. And it might even be unconstitutional. That is, if the witness claims the suspect is male, then the lineup is no good if it consists of four females and one male.
More natural exposition
You don’t have to dump a garbage can full of expository data in the first sentence. A female pronoun or name can give away gender. A nickname might indicate age, such as Junior or Grandma. Maybe you can comment on agility or speed or fatigue in order to get physical condition across. And height can come up fairly naturally if your character has to reach something on a high shelf, or look up or down at another character. Or maybe they have to determine if they’re tall enough to get onto an amusement park ride.
Any of these is better than a list of vital statistics. Those don’t really come up naturally unless you’re writing about medicine or, maybe, a beauty pageant or a sporting competition.
Describe aliens very quickly. The basics should still be your guide. However, you might need to cover other issues, such as whether they can speak or hear, or whether they can breathe our air.
Give your readers as much of the picture as is necessary. Don’t describe the corners of the room unless you need to. But at least tell them there’s a room.